Process of regenerating an aqueous alkali solution



Patented Aug. 1, 1950 PROCESS OFRJEGE NERAT ING AQUEOUS j .ALKALI SOLUTION John Happel, Brooklyn land Stephen P. Cauley,

Jackson Heights, N. Y., assignors to Socony- Vacuum Oil. Company, Incorporated, a corporation of New York No=Drawing .ApplicationJune 11,1943. Serial No, 90,491

7 Claims. .1

This application is a continuation-in-part of our co-pending application Serial Number 463,688, filed October :28, 51942, for sweetening Hydrocarbons, now abandoned.

This invention is directed to the treatment of hydrocarbon oils for the reduction of the mercaptan suliur content thereof, "particularly intended to provide Ia finished gasoline fraction which is either isvveet"-- to the doctor'zt'est or-sis sufiiciently low in sulfur tobe acceptable under specifications wherein the doctor test is :not used and total sulfur content is deter mined. Stated in-another way, theinvention i's directed to =the treatment of a hydrocarbon 1 mixture containin mercap'tans to eflect a substantial removal of mercaptan or mercaptansulphur from the mixture. 7

In treating hydrocarbons; 'isuch-asstraightmun gasoline, natural gasoline, icra'cked gasoline :and the like, to render them sweet tothe doctor. test, the objective is to remove materials ofvthe nature of hydrogen sulfide, mercaptans or tl're like-or to'convert them to innocuous compounds. Washing with aqueous solutions of strong alkalies, such as causticsoda will remove-most or the hydrogen sulfide and-some, but not all, of the *mercaptans. Washing with aqueous caustic to which some material has been added as a soluti-zer, or solubility promoter, enables the caustic to dissolve and remove more-or ail-lot the mercaptans. Butyle'ne. glycols, but-yric acidsgand moval of mercaptancsulfur andsimilar acidic materials, that the mercaptans-may be. readily removed and the spent caustic solutionmay be regenerated for .re-use hy blowmg; with vair or other oxidizinglgas. r i A It is known that caustic soda solution is' a competent reagent for the removal of mercaptans ot low molecular weight and as such it finds is "capable, when used in sufiicient quantities, xo'f effecting such removal; .Morelusua'lly theicaustic solution is: re-enforced in its ability to remove the higher mercaptans by the addition. of materials spoken of in the 'artas solutizers becausefthey increasethe mercaptan removal power "or" the phenolic materialare so used. folder methods make use oisodiumplumbit'e forined bydissolving litharge in caustic soda,'the 'efiect here -heing to convert-mercaptans to m'ercaptides :and later to disu-lfides, which are-inhocuousto the doctor test, by addition of'free sulfur.

' "-In-general, allprocesses of this kind leavesomething to be desired, and this field, oneof'the old'est in petroleum'refining, is still the subject-of active research.

This invention has for its object theprovision hy droxy benzene derivatives hereinafter defined" be added to a'caustic solution which has been utilized or is to be utilized as a reagent for therecaustic. Many materials, including glycols, suc'l'i as butyl'ene glycol; monocarboxyli'c acids: such "as butyric- .aciol, and phenolic materials. "such "as cresol are so'used 'as'solutizers;

In all cases, 'howeveryit has been foundnecessary to regen'eratethe caustic solutions 'by steaming to remove m'ercaptans. "The're-lative cost ni this procedurefincreases sharply "as the 'mercap tan sulfur concentration of'the treating solution decreases. High regeneration costs of steaming therefore limit the flexibility of'treatingprocesses, intha't morereiabora'te"mercaptan' removalequipmentjmust be .used'in'iconiunction with regeneration 'by steaming than 'wouldfbe requiredwithifai more e'fficient method 'ofregeneration. v I f It has been found thatiwhen "certain'polfy hy-' droxy' benzene carboxylic acids. and'relat'edfcon'rpounds, of which group the preferred memberjils tannic acid,v are ,present in small amounts "in "the caustic solution whether with or without solutizers, that already, efiective andcheap-regeneraition -can be conduc'ted,,.runder certain. conditions hereinafter defined, by asimple-iprocess o'ffblow; ing with vair or other. oxidizing gases at atmosr phe ric. temperature. ,f

The process herein proposedithenisxone.where in. a gasoline. .or otherlighthydrocarboninaction contain-ing- ,mercaptan sulfur, islcontactedfiin an oxygen free contacting system ot the type, usual. in the industry witha causticialkali reagent-rot the type normally used for removal :of r-mercaptarr sulfur and the spent neagenttherefrom, with addedetannin .or relatedssuhstances external-11'} regenerated by blowing ormcontacting the-m en taming; gases. 1

arr-example; of: the kind; obliteration-whi h maybe.ohtained undentheseiconditi nsathe iole lowing-xexperimental-data:isisiven; H

A caustic-tannin solution of 10% NaOH 1% tannin (C. P.) which has been blown with air was used to tre-at' aj full".range'-.jcracked gasoline. The treating'was conducted in -an atmosphere of nitrogen to avoid internal regeneration and samples of gasoline were withdrawn at one minute intervals and analyzed for mercaptan sulfun; The data obtained are shown below.

u ur onsample tent, Wt. Per cent Raw Gasoline 0142 Gasoline after 1 minute contactin 0. 0078 Gasoline after 2 minutes contacting 0. 0064 Gasoline after 3 minutes contacting- 0.0058 Gasoline after 4 minutes contacting 0. 0055 *"Atthis point the treating solution was withdrawn and blown with air for'several minutes for regeneration. The treating solution was then returned to the treating flask and contacted as before. The following results were noted.

' catalyst. The following table gives a number of results obtained by this procedure:

TABLE I Mercaptan sulfur regeneration rates, percent/ min, 1 N Na p-cresylate solutions containing v 'n-butyl! mercaptan Constituent Cone, Per Tannin cent v 0 I 0. 003 0. 003 0. 25 U. 074 Q. 077 Q. 50 .0. 113 '0. 035 1. 00 O. 122 0. 136

- further. point of interest in connection with the regeneration is that this regeneration must notbe conducted to a point of complete conversion of mercaptides to disulfides since somewhat u ur .onm tent, Wt.

Per cent Gasoline from previous contacting 0.0055 Gasoline after-l minute contacting 0. 0036 Gasoline after 2 minutes coutacting- 0. 0033 Gasoline afterS minutes contacting 0. 0028 Gasoline after 4 minutes contacting 0. 0025 [The causticv solutionv may be either sodium hydroxide or potassium hydroxide and it will usually be a solution of a concentration between about 10% causticand 45% caustic. From the standpoint of efliciency, potassium hydroxide is to be'preferred. However, cost relationships will probably more usually indicate sodium hydroxide as the alkali to be used. The concentration of tannin or other catalytic agent in the treating solution may vary. It has been found that from 1% to 3% by weight appears to be the most effective concentration; although concentrations as low as 0.1% may be used. Onthe upper end, concentrations higher'than 5.0% appear at present to yield diminishing returns. The treating solution may be contacted with the petroleum fraction to be treated in any conventional treating system, such asfin a packed tower or any system providing countercurrently arranged contacti'ng stages." The amount of solution to be used, may be varied to; the individual treating requirements, but in general, will be from 1-50% by volume of the petroleum fraction being treated. The treating. temperature may vary. For pracbefore this point is reached, oxidation of the catalytic material itself occurs depriving it of further effectiveness. In general, however, the amount of residual mercaptan sulfur which must beallowed to remain is quite low, as indicated byTable IIiolloWing. The data, here presented is again derived from laboratory experiments which is quite parallel with commercial operation. .-:;..'I'1'le procedure used in conducting these tests was as follows: A solution containing five gram moles/liter of free NaOI-I,.one gram mole of sodium cresylate, and a. given concentration of oxidation catalyst is prepared for testing. A concentration of n-butyl mercaptan greater than necessary-for stabilization ispthen added to the the deviation in mercaptan concentration is approximately 0.2% by weight during each cycle. At thexend of seven cycles the solution is analyzed forzits catalyst content. If no appreciable reduction'in catalyst concentration is obi tained during the above operation the process is repeated using the same solution but at a lower ti'cal operation, a temperature of 75-400 F. is I recommended. Since this is quite a usual atmospheric temperature" or readily attainable around an oil refinery, this phase of the operation presents no difficulties.

*f'Certain other points are of' interest in connection with "this operation. First, the concentration of the catalytic material has an influence upon the rate of regeneration of the re-' agent. This 'infl'uence is shown by the data in Table I follow-ing,'"which data is derived from taining 1% of mercaptan sulfur, and the catalyst mercaptan concentration. Whenever the catalyst content isfound to have been appreciably reduced bythis procedure it is evident that'the mercaptan concentration present was not sulficient for catalyst stabilization. Results are given the following table:

TABLnn r Limitsof BSH cone. for protection of oxidation 1 catalysts I I. -[n-Butyl mercaptan used] I -Catalyst amen) Material Cone, Wt. Cone, Wt. Per cent Percent asiegssr From this it will be observed that a relatively small amount of residual sulfur amounting to not over -about 0.3% by weight, calculated'as mercaptan, of the caustic solutiongisamply suificient to protect the reagent.

This process has several very material advantages. Of major importance, the sulfur is actu'ally removed from the oil, and not merely-converted to the disulfide form. This is-of importanc'e since while disulfide sulfur is relatively-noncorrosive and not-objectionable from-the "stand- "of odor, it exercises a highly deleterious effect upon the lead susceptibility of the gasoline in which itis contained and consequently modern processing requires the removal rather than the conversion of sulfur. Another major featu're' is that the oxidation regeneration, instead of being a steaming regeneration may be accomplished by blowing with relatively low pressure air alt-ordinary temperatures, thus effecting a major reduction in cost. Of interest also is the fact that while steaming regenerations must be con ducted in regenerative equipment of the nature of a iractionating tower of considerable height, the-regeneration here spoken of may be conducted i-n-relatively simple equipment. Of further interest is the fact thatthe degree of'regeneration attained is such that the caustic solution may be or relatively low concentration and low viscosity and still operate at quite high removal efiiciencies, thus completely doing away with prior difficulties having to do with "entrained gasoline, emulsions, dilficulty of separating hydrocarbons from reagent, both during treating and during regeneration, encountered in those previous processes which required the use of reagents of high concentration.

The catalytic reagents utilized herein are of particular interest.

In general, we have found the poly hydroxy benzene. carboxylic acids and certain of their derivatives to be useful for this purpose. Such acids as the dihydroxybenzoic acids, including proto-catechuic acid and the resorcyclic acids,

and the trihydroxybenzoic acids such as gallic acid and its related compounds and derivatives are founduseful. However, a particular preferonce is had for those compounds known as tannin o'r tannic acid. The term tannic acid or tannin is understood to cover those substances generally so grouped. Most of them are subfi iaznc'es widely distributed in the vegetable kingdone. They are soluble in water, possess an acid, astringent taste, are colored dark blue or green by ferrous salts, precipitate gelatin, and form leather when applied to animalhides. The constitution of many tannic acids is still somewhat obscure. Some appear to be glucosides' of gal lic acid, and decompose into gallic acid and sugar upon boiling with dilute acids. Others contain phloroglucin. Upon fusing with KOH these mostly form protocatechuic acid and phloroglucin. Among the tannic acid compounds there may be named gallotannic acid, digallic acid, gallyl-gallic acid and the various tannin materials derived from oak-bark, quinine-bark, coffee, moringatannin, cutch, chestnut, logwood, sumac, and many other natural sources. Many such compositions appear to contain compounds of the" nature of polyhydroxyflavpinacols, yielding, upon fusion with alkali, poly hydroxy benzenes such as phloroglucin, resorcinol, or pyrogallol, and poly hydroxy benzene carboxylic acids such as protocatechuic or gallic acids. All such compounds Average Rc generation Slope; Ber Cent S(S' H), regent/mm.

Tannin Material Qucbrach'o ('0. W. Ext.) Tara--. Osage Orange Logwood #4 Ulm'o Quebracho Spruce n. w. Ext.)

It is apparent that all of these materialsmay be applied in the process and -give regeneration at useful rates, although the materials vary among themselves in efliciency.

It willbe noted that all of the compounds herein suggested as oxidation catalysts are eme. braced within the class of poly hydroxy benzene carboxylic acids and derivatives thereof; within this class it is preferred to use tannic-acidas hereinabove defined.

'Weclaim:

*1. The process of regenerating an aqueous alkali solution containing weakly acidic sulphur compounds and a small amount of an oxidation promoterwhich catalytic'al-ly promotes the oxidation of said weakly acidic sulphur compounds, andwhich itself is capable of air oxidation, substantially consisting of a .polyhydroxy benzene carboxylic acid having more than two hydroxy groups and capable, of oxidation to a quinone form, which solution has been used toex-trac't said weakly acidic sulphur compounds from. hy drocarbon fluids, comprising; contacting said solution with anroxy'e'en-contaimng gas in such manner as to oxidize "said sulphur compounds but 'to leave suflicient amount of *unoxidizedsu-lphur compounds in said solution to substantially reduce oxidized promoter that may be formed to the original catalytic form and removing the oxidized sulphur compounds from solution.

2. The process of regenerating an aqueous alkali solution containing weakly acidic sulphur compounds and a small amount of an oxidation.

promoter which catalytically promotes the oxidation of said weakly acidic sulphur compounds, and which itself is capable of air oxidation, substantially consisting of a tannin, which solution has been used to extract said weakly acidic sulphur compounds from hydrocarbon fluids, comprising: contacting said solution with an oxygencontaining gas in such manner as to oxidize said sulphur compounds butto leave sufiicient amount of unoxidized sulphur compounds in said solution tosubstantially reduce oxidized tannin that may be formed to the original catalytic form and removing the oxidized sulphur compounds from solution. I 1

k 3. The process of regenerating an aqueous alkali solution containing weakly acidic sulphur compounds and a small amount of an oxidation promoter which catalytically promotes the oxidation of said weakly acidic sulphur compounds, and which itself is capable of air oxidation, substantially-consisting of gallic acid, which solution has been used to extract said Weakly acidic sulphur compounds from hydrocarbon fluids,

comprising: contacting said solution with an oxygen-containing gas 'injsuch manner as to oxidize said sulphur compounds but to leave s'ufiicient amount of unoxidized sulphur compounds in said solution to substantially reduce oxidized gallic acid that may be formed to the original catalytic form and removing the oxidized sulphur compounds from solution.

4. The process of regenerating an aqueous alkali solution containing weakly acidic sulfur 'compoundsand a small amount of an oxidation promoter which accelerates the rate of oxidation of said weakly acidic sulfur compounds in the presence of oxygen and which itself is deactivated by air in the absence of a minimum concentration of said weakly acidic sulfur compounds, substantially consisting of a tannin, which solution has been used to extract said weakly acidic sulfur compounds from hydrocarbon fluids, comprising: contacting said solution with an oxygen-containing oxidizing gas until a substantial portion of said weakly acidic sulfur compounds is oxidized-shut at least about 0.1 per cent of unoxidized weakly acidic sulfur compounds and sumcient'to maintain the activity of said tannin remains in said solution, and removing the oxidized sulfur compounds from the solution.

5. The process of regenerating an aqueous alkali solution containing weakly acidic sulfur compounds and a small amount of an oxidation promoter which accelerates the rate of oxidation of said weakly acidic sulfur compounds in the presence of oxygen and which itself is deactivated by air in the absence of a minimum concentration of said weakly acidic sulfur compounds, substantially consisting of gallic acid,

which solution has been used to extract said weakly acidic sulfur compounds from hydrocarbon fluids, comprising: contacting said solution with an oxygen-containing oxidizing gas until a substantial portion of said weakly acidic sulfur compounds is oxidized but at least about 0.1 per cent of unoxidized weakly acidic sulfur compounds and sufficient t maintain the acitivity of said gallic acid remains in said solution, and

removing the oxidized sulfur compounds from the solution. J. 6. The process of regenerating an aqueous alkali solution containing weakly acidic sulfur compounds and a small but effective amount of an oxidation promoter selected from the group consisting of gallic acid, tannic acid and tannins, which promoter accelerates the rate of oxidation of said weakly acidic sulfur compounds in the presence of oxygen, said solution having been used to extract said weakly acidic sulfur com-. pounds from hydrocarbon fluids, comprising: contacting said solution with an oxygen-containing oxidizing gas until a substantial portion of said weakly acidic sulfur compounds is oxi; dized but at least about 0.1 per cent of unoxidized weakly acidic sulfur compounds remains in said solution, and removing the oxidized sulfur com: pounds from the solution. -'7. The process of regenerating an aqueous alkali solution containing weakly acidic sulfur compounds and a small but effective amount of an oxidation promoter selected from the group consisting of gallic acid, tannic acid and tannins, which accelerates the rate of oxidation of said Weakly acidic sulfur compounds in the presence of oxygen, said solution having been used to ex tract said weakly acidic sulfur compounds from hydrocarbon fluids, comprising: contacting said solution with an oxygen-containing oxidizing gas until a substantial portion of said weakly acidic sulfur compounds is oxidized but about 0.2 to about 0.3 per cent of unoxidized weakly acidic sulfur compounds remains in said solution, and removing the oxidized sulfur compounds from the solution.

'JOHN HAPPEL.

STEPHEN P. CAULEY.

REFERENCES CITED The following references are of record in file of this patent:

UNITED STATES PATENTS the Hungary Mar. 17, 1941 

6. THE PROCESS OF REGENERATING AN AQUEOUS ALKALI SOLUTION CONTAINING WEAKLY ACIDIC SULFUR COMPOUNDS AND A SMALL BUT EFFECTIVE AMOUNT OF AN OXIDATION PROMOTER SELECTED FROM THE GROUP CONSISTING OF GALLIC ACID, TANNIC ACID AND TANNINS, WHICH PROMOTER ACCELERATES THE RATE OF OXIDATION OF SAID WEAKLY ACIDIC SULFUR COMPOUNDS IN THE PRESENCE OF OXYGEN, SAID SOLUTION HAVING BEEN USED TO EXTRACT SAID WEAKLY ACIDIC SULFUR COMPOUNDS FROM HYDROCARBON FLUIDS, COMPRISING: CONTACTING SAID SOLUTION WITH AN OXGEN-CONTAINING OXIDIZING GAS UNTIL A SUBSTANTIAL PORTION OF SAID WEAKLY ACIDIC SULFUR COMPOUNDS IS OXIDIZED BUT AT LEAST ABOUT 0.1 PER CENT OF UNOXIDIZED WEAKLY ACIDIC SULFUR COMPOUNDS REMAINS IN SAID SOLUTION, AND REMOVING THE OXIDIZED SULFUR COMPOUNDS FROM THE SOLUTION. 